The asphaltic paving, binding and roadway arts have had as an objective for many decades the provision of suitable road building and paving materials with minimum amounts of asphalt presence. A continuing need exists for technology which will provide low asphalt content binders, paving fillers, coatings and the like. In addition, the industry requires new emulsion systems which will allow the production of these materials in combination with suitable mineral aggregate without the high energy input generally required in asphaltic paving. A need exists for stable low asphalt emulsions. Paving binders are frequently in the form of emulsions requiring high loads of solvents and asphalt. These emulsions are heated with considerable mixing, grinding, and milling with suitable aggregate materials for application in building and repairing roads, streets, and parking lots. The requirements for paving repair have also created a need for a paving mixture which can be made at substantially lower temperatures by use of an emulsion of asphalt and aggregate.
Many emulsions of asphaltic materials, including aggregate, sand, and the like have been or are presently being used in the industry, however, these emulsions continue to have limitations, either in their stability or the economic use of asphalt. In order to avoid considerable energy input in the form of heat and milling of asphaltic paving materials, the art has utilized various solvents and soaps in order to produce a mixable emulsion of asphalt and aggregate materials.
On the other hand, asphaltic paving compositions and the like continue to be prepared through the use of heating up to 250.degree. F. and greater with substantial milling in colloidal mills with water solution and gelling agents, wherein the concentration of asphalt is substantially over the 25-50% by weight range. Even with these significant energized forms of asphalt, gels are required in order to enhance the coatability of the aggregate. Bituminous emulsions used as binders in forming paving compositions are well known in the prior art and are in wide commercial use. The maximum limit of the bitumen that can be employed in such emulsions is about 75%. With various gels, this percentage can be raised but substantial energy input is required for the formation of the paving composition from these emulsions which are combined with aggregate material. Common gelling agents are comprised of soaps, either partially or fully saponified. A variety of such gelling agents can be employed in making bituminous gel. For example, a mixture of rosin and fatty acids react with from about 4 to about 25% of a base, e.g., sodium hydroxide, potassium hydroxide, and ammonium hydroxide, or the like. Tall oil and tall oil pitch have been broadly used in the art, which when combined with from about 4-10% of a base such as sodium hydroxide forms a suitable soap filling agent.
More recently, rapid setting emulsions have been provided by mixing asphalt with tall oil, tall oil derivitives or mixtures thereof, and combining and mixing said mixture with treated water, comprising tall oil, tall oil derivatives, and mixtures thereof with strong base, and water. In other methods, rapid setting emulsions are produced by mixing asphalt, copolymers of styrene-butadiene-styrene block and styrene isoprene-styrene block, petroleum distillate, and mixing and combining the asphalt copolymer, petroleum distillate mixture with water, containing tall oil, tall oil derivatives, or mixtures thereof, strong base and water. These rapid setting emulsions are used primarily in surface treatment, such as chip seal coats. Such emulsions are also useful for penetrating treatment of macadam, as sand seal coats, and tack coats to promote adhesion of overlays.
The treatment of pavement surfaces for the rapid setting high-float asphalt emulsion are taught to require a substantial percent by weight of asphalt content, for example, 50-75%, as well as presence of anionic emulsifiers, tall oils, and other organic materials, such as acid esters, which in the presence of a pH greater than about 9 generally created by the presence of sodium hydroxide, potassium hydroxide, and the like, provide gelling agents which are either partially or fully saponified.
Additional work is reported suggesting that pH and electrolyte concentration in an aqueous phase, plays a major role in the stability of water-in-petroleum and residual oil emulsions. It is also suggested that unequal effect on the degree of emulsion collapse is due to pH change in the systems, both before the emulsion is formed and after the emulsion formation.